"Microsoft and Perceptive Pixel Inc. (PPI) today announced that they have entered into a definitive agreement under which Microsoft will acquire PPI, a recognized leader in research, development and production of large-scale, multi-touch display solutions." Yes, Jeff Han is now a Microsoft employee. This demo still amazes me - from 2006. Before the iPhone. Before Android. Before the iPad. Remember that the next time you wind up in a discussion about who supposedly invented what.

It's a standard whiteboard, nothing electronic in it, used with special markers and a detector on the side. It records everything written on the whiteboard to a program.

I've seen this same system hooked up to projection screen and used to interact with a windows desktop.

There's a simple way to test this hypothesis : tap the whiteboard with your finger. If the surface is soft, you are likely dealing with a resistive touchscreen. If nothing happens, the system likely detects the stylus in particular, which is generally done using Wacom-like inductive sensors. If your finger tap is indeed detected, you may be onto something there...

"There's a simple way to test this hypothesis"
I don't have access to one now, so I can't tell you.

Up to now I was thinking about the "pen" containing an emitter and having sensors on the side. However it seems the opposite should be equally feasible and far more scalable.

An example might be to go to a football field, broadcast different frequencies at each corner and place a wireless microphone on players. A computer could listen to an arbitrary number of mic's on the field, pinpointing them on a map by analysing audio timing and/or phase differences. Kind of like a localised "GPS" built out of commodity audio equipment.

This could be used to help in statistically analysing athletic behaviour and recognising trends to gain a competitive advantage. Even speed could be recorded accurately using doppler effects. Probably been done, but would be neat to experiment with.